Tremolo effect producing acoustic filter system

ABSTRACT

The apparatus of the invention comprises a loudspeaker, preferably, having a nearly flat diaphragm, and a plurality of microphones disposed in confronting relationship to the diaphragm of the loudspeaker at different positions in a sound radiation plane of the diaphragm, so that the microphones can individually pick up sounds radiating from different portions of the diaphragm where vibrational modes are expected to be different from one another. Further to finish a tremolo effect to the sounds finally produced, the sound waves from the loudspeaker to the microphones are periodically interrupted. According to one example of the invention, such periodical sound interruption may be caused by rotating the loudspeaker itself, and according to another example thereof, there may be employed a sound interrupting member having therein sound passages for selectively and locally passing the sound waves emitted from the different portions of the loudspeaker to the respective microphones, such sound interrupting member being disposed rotatably between the loudspeaker and the microphones.

[4 1 Oct. 15, 1974 [54] TREMOLO EFFECT PRODUCING ACOUSTIC FILTER SYSTEM[75] inventor: Eisaku Okamoto, Hamakita, Japan [73] Assignee: NipponGakki Seizo Kabushiki Kaisha, Shizuoka-ken, Japan [22] Filed: July 16,1973 [21] Appl. No.: 379,317

[30] Foreign Application Priority Data July 18, 1972 Japan 47-84573 July20, 1972 Japan 47-85492 [52] US. Cl 179/1 J, 179/1 D, 84/125 [51] Int.Cl. H041 l/02, H04r 1/20 [58] Field of Search 179/1 .1, 1 AT, 1 D;

181/31 A, 31 B, 31 R, .5 F; 84/125 [56] References Cited UNITED STATESPATENTS 3,346,070 10/1967 Hare 179/1 J 3,506,773 4/1970 George 179/1 JPrimary Examiner--Kathleen H. Claffy Assistant Examiner-Douglas W. OlmsAttorney, Agent, or Firm-Cushman, Darby & Cushman {57] ABSTRACT Theapparatus of the invention comprises a loudspeaker, preferably, having anearly flat diaphragm, and a plurality of microphones disposed inconfronting relationship to the diaphragm of the loudspeaker atdifferent positions in a sound radiation plane of the diaphragm, so thatthe microphones can individually pick up sounds radiating from differentportions of the diaphragm where vibrational modes are expected to bedifferent from one another. Further to finish a tremolo effect to thesounds finally produced, the sound waves from the loudspeaker to themicrophones are periodically interrupted. According to one example ofthe invention, such periodical sound interruption may be caused byrotating the loudspeaker itself, and according to another examplethereof, there may be employed a sound interrupting member havingtherein sound passages for selectively and locally passing the soundwaves emitted from the different portions of the loudspeaker to therespective microphones, such sound interrupting member being disposedrotatably between the loudspeaker and the microphones.

8 Claims, 18 Drawing Figures PATENIEHIH 3.842.205

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M 7 (IP M M m K/I EY KS 0 E (NM OE TG FREGUENCY(Hz) AMP TREMOLO EFFECTPRODUCING ACOUSTIC FILTER SYSTEM BACKGROUND OF THE INVENTION 1. Field ofthe invention The present invention relates to sound production systemscapable of producing tremolo effects and tone coloring effects, and,more particularly, to novel tremolo effect producing acoustic filterapparatus of compact structure and also providing desired tone coloring,which are most suitable for use with electronic musical instrument.

2. Description of the prior art Many tone coloring devices haveconventionally employed electrical filter circuits composed of onlyelectronic components such as resistors and capacitors. Tone colorsproduced by such an electrical tone coloring device are poor in varietyand variations, and are less in acoustic interest.

For good understanding of the prior art device an example of theconventionally used tone coloring means is now discussed with referenceto FlG. 1. ln FlG. 1, an audio signal from keyers, for example, of anelectronic mucical instrument or other program sources is fed through aninput terminal to a pre-amplifier circuit A, and amplified thereby, andthen this amplified audio signal is supplied to a tone coloring circuitwhich comprises a low pass filter F a band pass filter F and a high passfilter F in parallel connection and individual variable resistanceresistors R R and R having one ends connected in series with therespective filters F F and F 3 at their output ends and having the otherends connected at a common juncture and for mixing the outputs of thefilter circuits F F and F at a desired ratio of mixing. At the commonjuncture will be developed in mixed condition three kinds of audiosignals respectively having different frequency to level characteristicsi.e., different frequency ranges as shown by f,, f and f in FIG. 2.These mixed audio signals are fed to a power amplifier A and therebyamplified and then reproduced by a loudspeaker SP.

Thus, in the conventional tone coloring device, the frequencycharacteristics of the reproduced sound wave are inherently determinedby the frequency band characteristics of the filter circuits employedand the parameters of the mixing variable resistance resistors.Therefore, the tone coloring device employing electrical circuits alonehas a great disadvantage in that a realistic and interesting soundresembling that of a natural musical instrument may not be obtainedsince the reproduced sound wave fails to be rich in variety.

As the conventional sound reproducing system for producing a tremoloeffect on sounds as they are generated by an electronic musicalinstrument, there is known the type having a rotational disc located infront of a loudspeaker or speakers to thereby provide a tremolo effect,as disclosed in, for example, Japanese Utility Model Publication No.22436/1965 and US. Pat. No. 3,204,722.

Said Utility Model Publication, as shown in FlG. 3, discloses a tremoloeffect producing apparatus comprising a motor 1, a rotary shaft 2operatively connected with the motor, an acoustic reflecting plate 3 ofwhich the center is supported by the end of the shaft so as to berotatable in any plane involving the shaft, a bearing 4 slidably engagedwith the shaft 2, a connecting lever 5 connecting the bearing 4 with theside portion of the reflecting plate 3, and a loudspeaker 6 in front ofwhich is located the reflecting plate 3 so as to face it, whereby thesounds from the speaker provides a tremolo effect through the reflectingplate as the plate is rotated with respect to the direction of theshaft, namely, axially of the loudspeaker.

Said US. patent, as shown in FIGS. 4 and 5, discloses another system forgenerating a tremolo effect on the sound waves from speakers including asound reproducing speaker enclosing cabinet, a vertically disposedspeaker supporting panel spaced inwardly from an open side of thecabinet, a plurality of sound reproducing speakers 6 mounted on thepanel, a rotating disc 7A spaced from and operating in a plane parallelwith the speaker supporting panel and having openings corresponding indiameter to the diaphragms of the speakers or a rotating plate 78 havingcutouts and a motor for rotating the disc or the plate at a requiredrevolution speed.

Another known device of the type in which a plurality of speakers arerotated in a plane to produce a tremolo effect and a vibrato effect isreferred to in the following two US. patents. That is, US. Pat. No.3,100,024, as shown in FIGS. 6 and 7, discloses an apparatus forproducing vibrato or tremolo effects, comprising a motor 1, a drum 8arranged on the inside of a peripheral wall on which a plurality ofspeakers 6 are revoluvably mounted for rotation about an axis, the drumbeing operatively connected with the motor through a belt so as to berotated, and slip rings R through which low frequency currents aresupplied to the respective speakers, whereby the sounds from thespeakers are given vibrato or tremolo effects as these speakers arehorizontally rotated in the same plane with that of rotation of the drumdriven by the motor.

As shown in FIG. 8, US. Pat. No. 3,084,585 indicates an acousticmodulator comprising a speaker mounting disc 9 having circumferentiallydisposed plural speakers 6 which may be rotated about a horizontal axis,namely, circumferentially by means of a suitable motor MA and may berotated about a vertical axis of a vertical standard 1C, namely,perpendicularly to the vertically diametric direction of the disc, bymeans of another motor MB, to produce a Doppler effect and a tremoloeffect.

However, these known tremolo effect producing systems have the followingdisadvantages.

First, the known tremolo effect producing apparatus are inconvenientlybulky, occupying a large space and complicated in mechanism and areimpossible to effectively produce a tremolo effect when reproduced bymeans of headphones in an electronic musical instrument. Furthermore,when incorporated in an electronic musical instrument, such an apparatusgenerally requires a fixed loudspeaker for sound reproduction havingnon-tremolo effect, as well as a rotating loudspeaker for providing atremolo effect, and also separate power amplifiers therefor.Accordingly, such an apparatus not only tends to be very expensive butalso is impossible to radiate tremolo and non-tremolo sounds from thesame loudspeaker, resulting in the lack of naturalness of sound in theperformance of the electronic musical instrument.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide a novel electro-acoustic system for producinginteresting tremolo and tone coloring effects which are quite close tothe sound effects of a natural musical instrument.

Another object of the present invention is to provide a tremolo effectproducing apparatus with tone coloring effects suitable for use with anelectronic musical instrument, which comprises, a closed housing or asealed box containing therein a sound radiating member such as aloudspeaker, a plurality of microphones opposed to a sound radiatingsurface of the loudspeaker at different positions, and a rotatable soundinterrupting member disposed between the loudspeaker and the pluralityof microphones so as to be quite close to both and having openings orcutouts constituting sound passages for passing sound from theloudspeaker to said microphones, and a drive means for rotating thesound interrupting member at a desired speed of revolution, whereby anaudio signal applied to the loudspeaker of the apparatus is reproducedinto a sound wave and then the sound wave is modulated by means of therotating sound interrupting member and picked .up by the microphones tothereby produce electrical audio signals having tremolo effects rich invariety, the individual signals thus produced also having differentfrequency ranges i.e., different tone colors due to the difference invibration mode at different locations in the diaphragm of theloudspeaker.

Still another object of the present invention is to provide a tremoloeffect producing apparatus capable of concurrently providing desiredtone coloring, which is of the arrangement comprising a rotatable soundradiating means such as a loudspeaker disposed in a closed chamber, anda plurality of sound pickup means such as microphones arranged in asound radiating plane of the loudspeaker at different locations thereofin the vicinity of the diaphram of the loudspeaker, whereby an audiosignal from a tone generator is reproduced by the rotating loudspeakerinto a sound wave and this sound wave is picked up by the individualmicrophones at different positions as sound signals, so that each soundsignal thus obtained has a tremolo effect due to the rotation of theloudspeaker and concurrently has a specific frequency range (or aspecific tone color) due to the difference in vibration mode at aportion of the diaphram of the loudspeaker.

Yet another object of the present invention is to provide a tremoloeffect producing system with acoustic filters, which is small in sizeand is compact and is simple in construction, and is possible todispense with such a conventional specifically designed loudspeaker ashas been used exclusively for obtaining a tremolo effect in anelectronic musical instrument.

A further object of the present invention is to provide a system forproducing a tremolo effect with tone coloring, which is suitablyadaptable for a headphone when it is used as a sound radiating system ofan electronic musical instrument.

A significant object of the present invention is to provide a tremoloeffect producing acoustic filter device comprising: a sound reproducingmember such as a flat-type loudspeaker capable of radiating a sound wavein full range and having different frequency characteristics inaccordance with the position of the sound radiating portion such as adiaphram; a plurality of microphones disposed at different positions inthe foreground of said sound radiating portion so as to pick uppositional variations in the frequency characteristics of the radiatingportion of the sound reproducing member; thereby constituting acousticfilters and a drive means for rotating the sound radiating member,whereby producing a tremolo effect in a picked-u audio signal. a

A still further object of the present invention is to provide a musicalsound reproduction system utilizing the above-mentioned specific tremoloeffect producing acoustic filter device of the electro-acoustic type inwhich an audio signal from the sound program is acoustically processedinto one having desired tremolo effects and tone colors and then isreproduced into a musical sound, so that the reproduced sound effectsgive the listener a realistic sound image without any impression of anartificial electrical sound.

Other objects, features and advantages of the present invention willbecome apparent from the following detailed description of somepreferred embodiments only by way of example when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagramillustrating an example of the conventional acoustic filter circuitsystem.

FIG. 2 is a chart of frequency characteristic curves for explaining thefilter circuit system of FIG. 1.

FIGS. 3 through 8 are structural views illustrating some examples of theconventional tremolo effect producing devices.

FIG. 9 is a schematic diagram showing the construction of an embodimentof the present invention.

FIGS. 10A, 10B and 10C are, respectively, an oblique view, a perspectivesection and a longitudinal section of a sound interrupting rotary memberused in the embodiment of FIG. 1.

FIG. 11 is a view, partly in section, of a modification of the rotarymember in the closed housing of the preceding embodiment.

FIG. 12 is a plan view of the rotary member illustrated in FIG. 11.

FIG. 13 is a schematic diagram showing another embodiment of the presentinvention.

FIG. 14 is a view showing the positional relation between theloudspeaker and the individual microphones of the present tremoloeffect-producing acoustic filter device.

FIG. 15 is a chart of frequency characteristic curves for explaining thepresent invention.

FIG. 16 is a schematic diagram of a further modification of the presentinvention.

In the drawings, like reference numerals and letters indicate like partsthroughout the embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 9, thereis schematically illustrated an electronic musical instrument circuitsystem incorporating the present invention, which comprises: a tonegenerator circuit 0 for generating audio signals; a key-operated keyingsystem K at which these audio signals are selected through tone keyersby the key operation of the player of the instrument; an amplifiercircuit A for amplifying the selected audio signal; a tremolo effectproducing acoustic filter assembly connected with the output end of theamplifier A to receive the audio signal from the tone generator circuitand thereby to produce audio signals each with a tremolo effect as wellas a tone color; a mixing circuit consisting of variable resistanceresistors for mixing individual audio signals derived from the acousticfilter assembly at a desired ratio; a power amplifier circuit A foramplifying the mixed audio signals; and a loudspeaker SP for radiating asound wave having the audio signals. The acoustic filter assemblyaccording to an embodiment of the present invention includes a closedbox or a hermetically sealed housing B within which loud speaker SPhaving, preferably, a nearly fiat diaphragm driven by the audio signalfrom the pre-amplifier A is fixedly disposed on one side of the interiorof the housing and also a plurality of microphones M M and M aredisposed opposite to the sound radiating surface of the loudspeaker SPat different positions in the same plane relative to one another. Amicrophone housing member D having parallel arranged compartmentstherein is provided on the other side of the interior of the housing B.Each compartment is open at one end and accommodates one of themicrophones, thereby preventing them from their acoustically interferingwith each other.

The housing B rotatably mounts therein a sound wave interrupting member13 between the radiating surface of the loudspeaker SP and themicrophone housing member D supporting therein the microphones M M and MThe sound wave interrupting member 13 are mechanically connected with adrive motor 10 so that it may revolve about an axis perpendicular tothat of the loudspeaker SP at a speed of 0.5 l5 revolutions per second.

At the resepctive output ends of the microphones M M and M are connectedindividual variable resistance resistors R,, R and R at each one end theother ends of which are connected at a common junction to thereby mixthe outputs derived from the respective microphones. The mixed audiosignal is amplified by the power amplifier A and reproduced by theloudspeaker SP into a desired sound wave.

The sound wave interrupting member 13 may be a cylindrical solid bodyhaving therein a plurality of diametrical openings or through-holes 13Awhich are in parallel relation with each other only at each open end ofthe cylindrical surface of the body as shown in FIGS. A and 108. Eachopening in the member 13 corresponds to one of the microphones M M and MEach sound passage 13A may be formed in the cylindrical solid body 13 topass sound therethrough in an arbitrary manner, for example, as shown bya section in FIG. 10C.

In any case, the openings or through-holes 13A are so formed that whenone end of each opening 13A comes close to the loudspeaker diaphragm,the other end of the opening 13A is confronted with the correspondingmicrophone M M or M thereby passing the sound waves from the loudspeakerthrough the opening 13A to the microphone. The plurality of openings 13Aare further so arranged as to correspond to different portions of theloudspeaker diaphragm where vibrational modes are expected to bedifferent from one another. When the member 13 is rotated, the soundpassages 13A are periodically formed and interrupted between theportions of the loudspeaker diaphragm and the respective microphones,whereby the sound waves emitted from the loudspeaker to the microphonesare given fade-in and fade-out effects, resultantly heard as tremoloeffect sounds.

Referring now to FIG. 11 a modification of the acoustic filter assemblyof FIG. 9 is illustrated, in which a rotary disk 13 is used in place ofthe rotational cylindrical body 13. This disk 13 has curved elongateopenings or cutouts 13B perforated along the circumference of the diskat different positions in its radius direction and provided at positionscapable of confronting the respective microphones M M and M as shown forexample in FIG. 12. The sound wave interrupting disk 13 is mountedbetween the loudspeaker SP and the microphones M M and M in such a waythat it may revolve about a shaft 14 disposed in parallel to the axis ofthe loudspeaker SP by means of the drive motor 10 through a belt 11 anda pulley 12.

Now, the operation of the assembly thus constructed will be describedhereunder.

As will be appreciated from the construction of the acoustic filterassembly as shown in FIG. 9 or 11, the microphone M, disposed oppositeto the radiating surface of the flat-type loudspeaker SP in the vicinityof its end portion receives an input sound wave of relatively lowerfrequency band components substantially below 400 Hz from theloudspeaker SP whose characteristic curve is shown by m in FIG. 15. Themicrophone M disposed opposite to an intermediate portion of theradiating surface of the loudspeaker SP receives an input sound wavehaving frequency components of a middle sound range of from about 500 Hzto about 5kHz, as shown by a characteristic curve m in FIG. 15, whilethe microphone M disposed opposite to the central portion of theloudspeaker SP receives a sound wave having relatively higher frequencyband components as shown by a characteristic curve m in FIG. 15.Acoustic filters are thus constituted and these filters can produce atremolo effect by rotating the sound interrupting member 13 or 13'.

Accordingly, when output signals from the respective microphones M M andM are mixed through the variable resistance resistors R R and R at thecommon juncture at a desired ratio, these signals are amplified by theamplifier A and fed to the loudspeaker SP for musical soundreproduction. Thus, from the loudspeaker SP there is obtained a soundwave which constitutes a musical sound having desired tone colors andtremolo effects.

Since the above-mentioned loudspeaker SP is not used for the listener tolisten directly to the sound wave produced therefrom, it may be of a lowreproduction power and a small size. The closed housing B employed mayalso be small in size.

The tremolo effect producing acoustic filter assembly enables therespective microphones M M and M to pick up audio signals havingdifferent frequency bands as illustrated by its filter characteristiccurves m,, m and m in FIG. 15 respectively.

FIG. 16 shows an example of a sound reproduction system utilizing thethus produced audio signals, in which the respective output terminals ofthe microphones M M and M;, are individually connected, via variableresistance resistors R R and R and power amplifiers A A and A to alow-frequency loudspeaker (woofer) SP an intermediate-frequencyloudspeaker (squawker) SP and a high-frequency loudspeaker (tweeter) SPrespectively, whereby the resulting sound waves from these loudspeakersprovide tone colors quite resembling those of natural musicalinstruments.

In the above embodiments of the tremolo effect producing acoustic filterassembly, it will be easily understood that a plurality of parallelyarranged microphones M,, M and M isolated acoustically and physicallyfrom each other may face to substantially one half of the soundradiating surface of the fixed loudspeaker SP within the closed housingB, and also that a number of directional microphones may be arranged ina manner as stated in connection with the microphones of the precedingembodiment.

Referring to FIG. 13, another embodiment of the present invention isillustrated in a schematic diagram of a sound producing system similarto that of FIG. 9, in which a closed housing B accommodates therein asmall loudspeaker of preferably an asymmetrically shaped, oblong, flattype diaphragm as shown in FIG. 14, mounted on a rotary shaft which issupported at one a side wall of the housing, and a sound shieldingcompartment member D mounting therein a plurality of directionalmicrophones M,, M, and M so as to be acoustically isolated from eachother. The shaft connected to the loudspeaker SP mounts thereon a pulley12 outside the housing B and is connected, via a belt 11 and a pulley12', with a drive motor which, in turn, is mounted outside the housing 8for rotating the loudspeaker. This loudspeaker SP,, can be rotated aboutits central axis at a speed of from 0.5 to 15 revolutions per second bythe motor 10 through the power transmission mechanism as mentionedpreviously.

The microphones juxtaposed in the compartment member D are seen to beopposite to and in proximity to the sound radiating surface of the flattype loudspeaker SP,,. These respective microphones are disposed atdifferent positions relative to each other with respect to the soundradiating surface as shown, for example, in FIG. 14. In this Figure, P,represents the driving point or voice coil of the flat type loudspeakerSP having an asymmetrically elliptic shape, and C represents therotational center of the sound radiating surface of the loudspeaker SPat which center this loudspeaker is supported by the rotary shaft forrevolution. An electrical signal picked up by each microphone M,, M, orM, is fed, through a variable resistance resistor R,, R or R and acommon juncture, to an amplifier A and then to a fixed loudspeaker SP.

The operation and effects of the above-constructed assembly forconstituting acoustic filters are substantially similar to those of FIG.9. That is, the microphone M, disposed in the vicinity of an end portionof the rotating flat loudspeaker SP,, picks up a sound wave ofrelatively low frequency components m,, whereas the microphone Mdisposed opposite to an intermediate portion of the sound radiatingsurface of the loudspeaker SP picks up a sound wave of intermediatefrequency components m and the microphone M disposed at a centralportion P, of the sound radiating surface picks up a sound wave ofrelatively high frequency component "1 thus constituting acousticfilters. The frequency characteristic curves given by m,, m and m, areas shown in FIG. 15. The picked-up signals are bestowed with tremoloeffects due to the rotation of the sound radiating surface of theloudspeaker SP The mixing resistors R,, R and R,, may be providedoutside the housing B as in the instance of FIG. 9. In this embodiment,the loudspeaker SP enclosed in the housing may be of a small outputpower and of a small size since it is not intended for being listened todirectly by the listener. The housing B also may be small in size. Theassembly of this embodiment is applicable also to the system shown inFIG. 16 with great advantages.

It will be understood from the foregoing statement that by theapplication of the present invention to, for example, an electronicmusical instrument, there are obtained sound waves which are felt to benatural when heard and which are free of the so-called feeling ofelectrified sound, but instead which present musical sounds quiteresembling those of natural musical instruments. Thus, it is possiblefor the listener to enjoy an interesting performance from an electronicmusical instrument incorporating this invention, so that the presentinvention provides varying highly sophisticated acoustic effects.

I claim:

1. A tremolo effect producing acoustic filter system comprising: aclosed housing, said housing including therein an electro-acoustictransducer having a sound radiating surface and capable of radiatingsounds having a desired frequency band, a plurality of acoustoelectrictransducers for picking up the sounds radiated from saidelectro-acoustic transducer and converting the sounds into electricsignals, said plurality of transducers being juxtaposed and acousticallyisolated from each other and opposed to the sound radiating surface ofsaid electro-acoustic transducer at different positions thereof, and arotary sound interrupting member disposed relatively closely betweensaid sound radiating surface of the electro-acoustic transducer and saidplurality of the acousto-electric transducers, said rotary soundinterrupting member periodically interrupting, in accordance with therevolution thereof, sound paths leading from said electro-acoustictransducer to said plurality of acousto-electric transducers, so as toprovide fade-in and fade-out effects and different frequency bandcharacteristics for the sounds picked up by the respectiveacousto-electric transducers; and means for giving rotation tosaid'rotary sound interrupting member at a required speed.

2. The system according to claim 1, in which said electro-acoustictransducer and said acousto-electric transducers are a loudspeaker andmicrophones, respectively.

3. The system according to claim 1, in which said rotary soundinterrupting member is of a cylindrical form having sound passagesprovided therein to open at different side surfaces thereof, saidpassages corresponding in number and position to said plurality ofacoustoelectric transducers.

4. The system according to claim 1, in which said rotary soundinterrupting member is a disc having cutout or opening patterns thereinto selectively form sound passages.

5. The system according to claim 2, in which said closed housing mountstherein a compartment member having juxtaposed compartments insidethereof each for accommodating each of said plurality of microphonestherein separately.

6. The system according to claim 2, in which said loudspeaker is of anearly flat type diaphragm.

10 tion, whereby the sounds picked up by the respective microphones maybe given fade-in and fade-out effects and also different frequency bandcharacteristics, re spectively.

8. The system according to claim 7, in which said loudspeaker is of aflat type and has a sound radiating surface of an asymmetricalconfiguration.

1. A tremolo effect producing acoustic filter system comprising: aclosed housing, said housing including therein an electroacoustictransducer having a sound radiating surface and capable of radiatingsounds having a desired frequency band, a plurality of acousto-electrictransducers for picking up the sounds radiated from saidelectro-acoustic transducer and converting the sounds into electricsignals, said plurality of transducers being juxtaposed and acousticallyisolated from each other and opposed to the sound radiating surface ofsaid electro-acoustic transducer at different positions thereof, and arotary sound interrupting member disposed relatively closely betweensaid sound radiating surface of the electro-acoustic transducer aNd saidplurality of the acousto-electric transducers, said rotary soundinterrupting member periodically interrupting, in accordance with therevolution thereof, sound paths leading from said electro-acoustictransducer to said plurality of acoustoelectric transducers, so as toprovide fade-in and fade-out effects and different frequency bandcharacteristics for the sounds picked up by the respectiveacousto-electric transducers; and means for giving rotation to saidrotary sound interrupting member at a required speed.
 2. The systemaccording to claim 1, in which said electro-acoustic transducer and saidacousto-electric transducers are a loudspeaker and microphones,respectively.
 3. The system according to claim 1, in which said rotarysound interrupting member is of a cylindrical form having sound passagesprovided therein to open at different side surfaces thereof, saidpassages corresponding in number and position to said plurality ofacousto-electric transducers.
 4. The system according to claim 1, inwhich said rotary sound interrupting member is a disc having cutout oropening patterns therein to selectively form sound passages.
 5. Thesystem according to claim 2, in which said closed housing mounts thereina compartment member having juxtaposed compartments inside thereof eachfor accommodating each of said plurality of microphones thereinseparately.
 6. The system according to claim 2, in which saidloudspeaker is of a nearly flat type diaphragm.
 7. A tremolo effectproducing acoustic filter system comprising: a hermetically sealed box,said box including therein a loudspeaker having a sound radiatingsurface with different positional frequency characteristics, and aplurality of microphones acoustically isolated and juxtaposed from eachother and opposed to said sound radiating surface at different positionsand disposed in proximity thereto; and means for giving rotation to saidloudspeaker at a required speed of revolution, whereby the sounds pickedup by the respective microphones may be given fade-in and fade-outeffects and also different frequency band characteristics, respectively.8. The system according to claim 7, in which said loudspeaker is of aflat type and has a sound radiating surface of an asymmetricalconfiguration.